The invention relates to a wheel loader with a lifting frame with Z-kinematics, which comprise an accessory arm with a lifting cylinder coupled to the vehicle frame or to the truck front-end and a rocker-type reversing lever coupled to the accessory arm, to the ends of which reversing lever the tipping cylinder and the connecting link are coupled for the swivelling of the attachment, whereby attachments, e.g. a bucket or a log loader, are mountable on the lifting frame.
A known wheel loader of this kind is shown in FIG. 8 of the drawing. With the latter, accessory arm 1 is designed H-shaped, whereby the lateral carriers parallel to one another are connected at their inner ends by means of articulated joints 2 to the truck front-end, which is usually connected by a folding articulated joint to the truck rear. The front ends of the lateral carriers are connected in an articulated manner by articulated joints 3 to an attachment, in the represented example of embodiment to a bucket 4. The lateral carriers are connected together in their middle region by a transverse tube 5 forming the H-web. Transverse tube 5 carries in its middle region cheeks 6 which are parallel to one another and form a bearing fork, between which cheeks reversing lever 7 of the Z-kinematics is mounted in the manner shown. The piston rod of tipping cylinder 9 is coupled in articulated joint 8 to one end of reversing lever 7, said tipping cylinder for its part being connected in an articulated manner by articulated joint 10 to the truck front-end. Connecting link 12 is connected in an articulated manner in articulated joint 11 to the other end of reversing lever 7, said connecting link being connected in an articulated manner by articulated joint 13 to the attachment. Accessory arm 1 is capable of swivelling about its articulated joint 2 by means of lifting cylinders 14, which are connected in a swivelling manner by articulated joints 15 to the truck front-end, whilst their piston rods are connected in a swivelling manner by means of articulated joints 16 to accessory arm 1.
Bucket 4 is shown in three different positions I, II and III in FIG. 8.
In position I, in which the bucket is in the area of the ground, the tipping cylinder engages via a large lever arm with reversing lever 7, so that the bucket can be swivelled without problem about its swivel axle 3 on the accessory arm. The situation changes, however, when the accessory arm is raised, when bucket 4 is intended to be swivelled between positions II and III. When accessory arm 1 is raised, tipping cylinder 9 in position II of the bucket tipped downwards engages solely via lever arm a with reversing lever 7. In position IIII of bucket 4 swivelled upwards, the effective lever arm b is enlarged, as can be seen from FIG. 8. In order to be able, in the presence of a high loading of the attachment, for example when a log loader is loaded, to swivel the latter between positions II and III with the raised lifting frame, high forces must therefore be applied by lifting cylinder 9, which however requires a large tipping cylinder 9, which is not necessary for the operation in other swivelling positions and therefore, apart from unnecessarily high costs, would also lead to unnecessarily high loading of the bolts and articulated connections, causing correspondingly greater wear.
The problem of the invention, therefore, is to provide a wheel loader of the type mentioned at the outset, with which, in a raised position of the lifting frame, the attachment can be swivelled with the necessary large moment from a position tipped downwards into a position tipped upwards, without any reinforcement of the tipping cylinder.